Phase modulation receiver



April 1937- M. G. CROSBY 2,076,175

' PHASE MODULATION RECEIVER Filed Oct. 23, 1935 2 Sheets-Sheet l llv PHA 6 E S/l/FTEI? ATTORNEY April 1937- M.'C 5. CROSBY 2,076,175

PHASE MODULATION RECEIVER Filed Oct. 25, 1955 2 Sheets-Sheet 2 BAND PASS I: AMPL.

BET.

INVENTOR I II-- MURRAY 6. caossv ATTORNEY Patented Apr. 6, 1937 UNITED STATES PATENT OFFICE PHASE MODULATION RECEIVER of Delaware Application October 23, 1935, Serial No. 46,285

22 Claims.

This application relates to a novel method and means for demodulating a wave modulated in phase at signal frequency. I do this by tuning the local oscillator or detector of a heterodyne receiver slightly off from synchronization 'so that the local oscillator and wave carrying carrier are approximately 90 degrees more or less than zero degrees apart. Demodulating waves in this manner has a disadvantage resulting from the fact that this slight off-synchronization adjustment which is required is more critical and difficult to maintain than the exact synchronization as used in the reception of amplitude modulated waves. The present invention also involves a new and improved method and means,

free of the defect mentioned above, for demodulating carrier waves modulated in phase. An additional feature of the present invention resides in automatic means for maintaining synchronization between the signal carrying wave and the dephased local oscillator used therewith to demodulate the same.

Another object of the present invention is to provide an improved means for holding a signal wave in relative synchronization with a local oscillator by means of an automatic frequency control device.

In receivers of the type disclosed in Crosby, United States appln. Ser. No. 616,803, filed June 13th, 1932, and Crosby United States application Serial Number 704,257, filed December 28th, 1933 wherein the signal of intermediate frequency is maintained in synchronization with an intermediate frequency oscillator, motor-boating of the automatic frequency controlled circuits may in some cases be encountered. In the present invention any tendency of motor-boating in the circuits is eliminated by applying signal energy to the local oscillator circuit to cause it to be entrained or pulled in step by virtue of its sympathetic oscillation tendency. I have found that this expedient removes any tendency of motor-boating in the circuit without limiting in any manner the efficiency of the circuits to demodulate the phase modulated wave.

Many other novel features of my invention and advantages arising from the use thereof will become apparent from the following detailed description thereof when read in connection with the attached drawings, in which:

Fig. 1 illustrates the essential features of a circuit arranged in accordance with my invention. In this circuit, phase or amplitude modulated waves from any source are applied to the differential detectors in phase opposition and also to a local oscillator to entrain the same to produce phase displaced oscillations to be applied in phase to the differential detectors. The system also includes a novel automatic frequency control circuit for controlling the frequency of the oscillator; while Fig. 2 shows somewhat more completely a receiver which is a modification of the receiver shown in Fig. 1.

In Fig. 1, I have shown a specific circuit arrangement which may be applied tothe output of a signal receiver of the radio frequency tuned type, or to the intermediate frequency amplifier of a signal receiver of the heterodyne type. In Fig. l, the phase modulated carrier wave of high frequency or intermediate frequency is fed from any source to the leads 4 coupled to the primary 1 of a transformer, the secondary winding 1 of which connects the control grids g of differential detectors l and 2 in push-pull relation. A local oscillator 3 having a tuned inductance l8 connected between its anode 5 and control grid ll supplies oscillations to an inductance 2| connected with a phase shifter l0 which in turn supplies energy of like phase to the suppressor grids gl of the differential detector tubes l and 2. The phase shifter Ill may be of any type known but is preferably of the type disclosed in my United States application Ser. No. 704,122, filed Dec. 27, 1933. Energy from the input leads 4 is also supplied by way .of the resistance of a potentiometer 8 and phase shifting line 9 to an inductance l6 and from the inductance It to the tuned inductance l8 of oscillator 3 to entrain the said oscillator. Phase shifters 9 and I0 may be of the same type, such as shown at 9 or may both be of the type disclosed in my United States application Ser. No. 704,122. All that is required is that they maybe adjusted so that the oscillator energy produced in 3 and supplied to 22 is normally 90 degrees, or 270 degrees out of phase with respect to the signal voltages appearing in transformer 1. The signal oscillations applied from I in phase opposition to the control grids g cooperate with the phase displaced oscillations supplied in phase from H] and 22 to the electrodes 9! to produce in the outputs of l and 2 amplitude variations characteristic of the signal. The operation of the differential detectors I and 2 will be apparent to one skilled in the art. The differential and in-phase voltages combine to produce a resultant energy the amplitude of which varies at signal frequency. This operation has been described in detail in several of my co-pending applications and in particular in my U. S. application Ser. No. 704,257, filed Dec. 28, 1933.

The differential detectors I and 2 demodulate or convert the phase modulations on the signal supplied from 1 into characteristic amplitude variations which may be supplied by coupling condensers C to the control grids of a pair of amplifier tubes I3 and I4 and from the anodes of tubes I3 and I4 to a jack I9 or connecting device by way of transformer I2.

The diiferential detectors I and 2 also furnish control voltages to operate the modulator tube 25. This voltage is supplied from the terminals of resistances I5 and I1 and acts through the inductance 29 to control the frequency of the oscillator 3. Suppose that the frequency supplied by 4 and 1 to the control grids g of I and 2 or from 3 to the suppressor grids gI of I and 2 starts to deviate so that the proper displaced synchronization is no longer maintained, the relative phases of the voltages on the control grids and the suppressor grids of the detectors changes, and an unbalance of the currents in the detector plates is caused. This unbalance causes a voltage to appear across resistors I5 and I1 which is passed by way of time control device 2! to the control grid 24 of modulator tube 25. This voltage varies the plate resistance of the modulator tube I8 and in turn varies the effective value of inductance 20 and consequently of the oscillator circuit I8 since the inductance 20 in the modulator plate circuit is coupled to the oscillator circuit inductance I8. The frequency and phase of the oscillations produced by 3 is changed the desired amount to correct the said deviation. Time constant circuit 2I removes the rapid phase variations resulting from the demodulating of the signal carrying wave which variations are due to the signal modulations thereon. Rapid variations due to signal modulation are passed by way of the coupling tubes I3 and I4 and combine in transformer I2. Slow variations result from frequency deviation of the signal of the local oscillator acting only on modulator tube 25.

For phase modulation reception, switch 23 is thrown to connect the anodes of tubes I3 and I4 in push-pull relation. For amplitude modulation reception, the anodes of tubes I3 and I4 are connected in parallel by switch 23. In both cases, the signal energy is made available at jack I9.

In Fig. 2, I have shown a somewhat more complete receiver which includes the principal features of the present invention as set forth in connection with Fig. 1. The circuit of Fig. 2, however, includes additional novel features which will now be described. Antenna 3|, radio frequency amplifier 32, detector 33 and bandpass amplifier and filter 34 tuned to an intermediate frequency with oscillator 41, constitute the main elements of a superheterodyne receiver. The output of bandpass filter 34 is connected as shown by way of a detector 35 and an automatic volume control circuit AVC to the control grids of one or more stages in the radio frequency amplifier. The rectified signal produced in 35 operates in a well-known manner to maintain a constant amplitude signal at the input of the amplitude limiter 36 connected with the output of intermediate frequency amplifier 34 so that the degree of limiting in 36 may be maintained constant. Oscillator 41 is the high frequency oscillator of the heterodyne receiver and supplies oscillations to the first detector 33 by way of line H.

The energy in the output of limiter 36 is fed by way of a push-pull transformer 38 to differential diode detectors 3!! and 40. An additional local oscillator comprises a tube 4! having its grid and anode electrodes connected as shown in frequency producing and determining circuits, including an inductance L and variable capacity C. This os-- cillator is entrained by energy supplied from the output of limiter 36 by way of a phase shifter 48 and the resistance of a potentiometer 49. The oscillator M in turn feeds oscillatory energy by way of blocking capacity X to the terminal of a radio frequency choke RFC connecting the oathodes of the differential diode detectors 39 and 40 to the differential resistors R1 and R2. The remaining terminal of R2 is connected to ground and by way of a secondary winding of 38 to the anode of 40. The remaining terminal of R1 is connected by the other secondary winding of 38 to the anode of rectifier 39. Oscillator M is entrained and held in step with the signal oscillations of signal energy fed thereto by way of the phase shifter 48 and potentiometer 49. As in the prior modification the synchronized oscillations produced by 4| may be phase displaced by or 270 degrees with respect to the signal carrying waves in the output of 36.

Operation of the differential diode detectors 39 and 40 is the same as the operation of the differential detectors of my United States application Ser. No. 616,803, filed June 13, 1932, and my United States appln. Ser. No. 704,257, filed Dec. 28, 1933. A variation in phase between the signal carrying energy of intermediate frequency from 38 and the intermediate frequency energy from oscillator 4! causes a voltage to appear across the series resistors R1 and R2 connected between the anodes of 39 and 40. Slow variations in the voltage is utilized as in Fig. 1, for automatic frequency control of the high frequency oscillator 41, and the fast variations (signal characteristic) changes appear across resistors R1 and R2 and are supplied by way of contact P and switch 54 and line 50 to the grid 5| of coupling tube 42 and from the anode 53 of said tube to any utilization circuit by way of jack 52.

For phase modulated wave reception, the switch 54 is thrown to position P so that the summation of the potentials in R1 and R2 is applied to the control electrode of 42. For amplitude modulated wave reception, the switch 54 is thrown to position A to utilize the voltage across R2 only and the limiter is cut out of the circuit by a switch 56.

The automatic frequency controlling voltage appearing across the terminals of resistors R1 and R2 is fed from one terminal of one of said resistors by way of time control device 45 to the control grid 60 of a modulator tube 58, the oathode of which is grounded as is one terminal of the other of the resistors R1 and R2. The anode circuit of tube 58 is connected by way of coupling condenser 44 to a point on the tuned circuit 59 regeneratively coupling the electrodes of the local oscillator 41. The automatic frequency control voltage passing through the time constant circuit 45 varies the plate resistance of tube 48 which in turn varies the effective capacity of coupling condenser 44 which is in shunt to the frequency determining circuit 59. In this manner, the tuning of the circuit 59 and consequently the frequency of the oscillator 41 is controlled in accordance with the voltages supplied to 59 by way of 44. 55 is a radio frequency choke by means of which voltage is fed to the anode of the modulator tube 58, while BP is a radio frequency by-pass condenser which completes the circuit including 44 in shunt to 59.

In either of the receivers of Figs. 1 and 2, the process of audio detection may be separate from that of automatic frequency control energy detection by providing separate detectors and adjusting the phase relation between the signal and oscillator by means of a phase shifter in either the signal or oscillator circuit. Such an arrangement would enable an audio detection with the phase between the signal and oscillator at a dinerent position than that required by the automatic frequency control detectors.

What is claimed is:

1. In a receiving system in combination, a signal carrying wave responsive device, a demodulator coupled thereto, a local oscillator coupled to said demodulator, a second demodulator coupled to said first named demodulator, a second oscillator, a circuit connecting said first demodulator to said second oscillator, phase shifting means in said last named circuit, a circuit connecting said second oscillator to said second demodulator, and a circuit connecting said second demodulator to said first named oscillator.

2. In a wave receiving system in combination, a signal carrying wave amplifying device, a demodulator connected thereto, a local oscillator coupled to said demodulator, an automatic volume control circuit connecting the output of said demodulator to said amplifying device, a pair of differential detectors having like electrodes connected in phase opposition to the output of said first demodulator, a second local oscillator, a

" phase shifting circuit coupling said second local oscillator to the output of said first demodulator, a circuit coupling said second oscillator in phase to like electrodes of said differential detectors, and a circuit coupling like electrodes of said differential detectors to said first named oscillator.

3. In a modulated wave demodulating system, a demodulator having input terminals energized by said phase modulated wave, said demodulator having output terminals, a local oscillator coupled to said demodulator, said oscillator including a frequency controlling reactance, a bandpass filter having input terminals coupled to the output terminals of said demodulator, said bandpass filter having output terminals, a pair of thermionic diodes each having an anode and a cathode, an alternating current circuit connecting the anodes of said tubes in phase opposition and to the cathodes, a direct current circuit including impedances connecting the anode electrodes of said diodes toa gether and to the cathodes, a coupling between the output terminals of said filter and said alternating current circuit, a modulator tube having a control grid, a cathode and an anode, a circuit connecting the control grid and cathode of said modulator tube to said impedances in the direct current circuit of said diodes, said last named circuit including time control elements, a reactive circuit connecting the anode to the oathode of said modulator tube and to said frequency controlling reactance of said oscillator, a second oscillator comprising a tube having its input and output electrodes connected in oscillation producing circuits, a phase shifting circuit having an input coupled to the output of said bandpass filter, said phase shifting circuit having an output coupled to said second named oscillator, a coupling between said second named oscillator and one of the circuits connected with the oathodes of said diodes, and a utilization circuit connected with the impedance in the direct current circuit of said diodes.

4. In a phase modulated wave demodulating system, a radio frequency amplifier, means for applying waves to be demodulated thereto, a demodulator coupled to said radio frequency amplifier, said demodulator having output terminals, a local oscillator having a tunable circuit coupled to said demodulator output terminals, a bandpass filter having input terminals coupled to the output terminals of said demodulator, said bandpass filter having output terminals, a pair of thermionic tubes each having an anode and a cathode, an alternating current circuit connecting the anodes of said tubes in phase opposition and to the cathodes of said tubes, a direct current circuit including impedances connecting the anodes of said tubes together and to the cathodes of said tubes, a coupling between the output terminals of said filter and said alternating current circuit, a thermionic modulator tube having a control grid, a cathode and an anode, a circuit connecting the control grid and cathode of said modulator tube to said impedances in the direct current circuit of said pair of tubes, said last named circuit including time control elements, a reactive circuit connecting the anode to the cathode of said modulator tube and. in parallel with the tunable circuit in said oscillator, a second oscillator comprising a tube having input and output electrodes connected in oscillation producing circuits, a phase shifting circuit having input terminals coupled to the output terminals of said filter, said phase shifting .circuit having output terminals, a coupling between the output terminals of said phase shifting circuit and the tube of said second named oscillator, a circuit coupling said second named oscillator to the impedances in said direct current circuit, and a utilization circuit connected with the impedance in the direct current circuit of said pair of tubes.

5. In a phase modulated wave demodulating system, a radio frequency amplifier having output terminals, means for applying Waves to be amplified thereto, a demodulator coupled to the output terminals of said radio frequency amplifier, said demodulator having output terminals, a local oscillator having a tunable circuit coupled to said demodulator, a bandpass filter having input terminals coupled to the output terminals of said demodulator, said bandpass filter having output terminals, an amplitude limiter having output terminals and having input terminals coupled to the output terminals of Said bandpass filter, a pair of tubes each having control electrodes, an alternating current circuit connecting said control electrodes of said tubes in phase opposition, a direct current circuit including impedances connecting the control electrodes of said tubes in phase opposition, a coupling between the output terminals of said amplitude limiter and said alternating current circuit,

a modulator tube having a control grid, a cathode and an anode, a circuit connecting the control grid and cathode of said modulator tube to said impedances in the direct current circuit of said pair of tubes, said last named circuit including time control elements, a reactive circuit connecting the anode to cathode impedance of said modulator tube in parallel with the tunable circuit in said oscillator, a second oscillator comprising an oscillator tube having input and output electrodes connected in oscillation producing circuits, a phase shifting circuit having input terminals coupled to the output terminals of said amplitude limiter, said phase shifting circuit having output terminals, a coupling between the output terminals of said phase shifting circuit and said second named oscillator, a coupling between said second oscillator and the direct current circuit connected with said pair of tubes, an automatic volume control circuit connecting the output of said bandpass filter to said radio frequency amplifier, and a utilization circuit connected with the impedance in the direct current circuit of said pair of tubes.

6. In a phase modulated wave demodulating system, a pair of tubes each having an auxiliary grid, a control grid, an anode and a cathode, an alternating current circuit connecting the control grids of said tubes in phase opposition, means for impressing the phase modulated wave to be demodulated on said circuit, an oscillator comprising an oscillator tube having input and output electrodes connected in oscillation producing circuits, a phase shifting circuit adapted to be energized by said phase modulated wave to be demodulated, said phase shifting circuit having output terminals, a coupling between the output terminals of said phase shifting circuit and said second named oscillator, a circuit connecting the auxiliary grids of said pair of tubes in parallel and coupling the same in like phase to said oscillator, and a utilization circuit connected with the anodes of said pair of tubes.

'7. In a phase modulated wave demodulating system, a pair of tubes each having an anode, a control grid, an auxiliary grid and a cathode, an alternating current circuit connecting the control grids of said tubes in phase opposition, a local oscillator having a tunable circuit including a reactance, a modulator tube having a control grid, a cathode and an anode, a circuit coupling the control grid and cathode of said modulator tube to the anodes of said pair of tubes, said last named circuit including time control elements, a reactive circuit coupling the anode and the cathode of said modulator tube with the tunable circuit of said oscillator, a circuit for impressing wave energy to be demodulated on said oscillator, a circuit coupling said oscillator to the auxiliary electrodes in said pair of tubes to impress oscillations of like phase thereon, and phase shifting means in one of said last two named circuits.

8. The method of demodulating a wave modulated in phase by means of a pair of detector tubes having a plurality of like control electrodes which consists in applying the said modulated wave energy to like electrodes in Said tubes in phase displaced relation, producing local oscillations, entraining the same with said wave energy in phase displaced relation, and applying said phase displaced locally produced oscillations in phase to like electrodes in said tubes.

9. The method of demodulating a wave modulated in phase by means of a pair of detector tubes having a plurality of like control electrodes which consists in applying modulated wave ener gy to like electrodes in said tubes in phase displaced relation, producing local oscillations, entraining the same with said wave energy in phase displaced relation, applying said phase displaced locally produced oscillations in phase to like electrodes in said tubes, and maintaining the frequency of said wave energy constant during said demodulation process.

10. The method of demodulating a wave modulated in phase by means of a pair of detector tubes having like electrodes and a receiving means including a tunable circuit which includes the steps of, applying signal carrying wave energy in phase displaced relation to like electrodes in said detectors, producing local oscillations, entraining the same with said signal carrying wave in phase displaced relation, applying said phase displaced oscillations in phase to like electrodes in said detectors, and controlling the frequency of said tunable circuit by energy produced in the outputs of said detectors.

11. The method of demodulating a Wave modulated in phase by means of a pair of detector tubes having a plurality of like control electrodes which consists in applying wave energy to be demodulated to like electrodes in said tubes in phase displaced relation, producing local oscillations, entraining the same with said wave energy in phase displaced relation, applying said phase displaced locally produced oscillations in phase to like electrodes in said tubes, and maintaining the frequency and amplitude of the wave energy to be demodulated constant during said demodulation process.

12. In a receiving system, a signal carrying wave energy responsive device, a demodulator coupled thereto and excited by signal carrying wave energy therein, a local oscillator, a circuit coupling said local oscillator to said demodulator to impress oscillations on said demodulator, a

circuit coupling said local oscillator to said wave energy responsive device to supply energy to said oscillator to entrain the same to oscillate at the frequency of the wave energy, and means in one of said circuits for displacing the phase of the oscillations impressed on said demodulator relative to the signal carrying wave energy impressed on said demodulator.

13. In a phase modulated wave energy receiving system, a phase modulated wave energy responsive device, a pair of demodulator tubes each having like input and like output electrodes, a circuit coupling the input electrodes of said tubes in phase opposition to said wave energy responsive device, a local oscillator, a circuit coupling said local oscillator to said wave energy responsive device to supply wave energy to said local oscillator to entrain the same to oscillate at the frequency of the said wave energy, a circuit coupling said oscillator to like input electrodes in said demodulator tubes to supply locally produced oscillations in phase to said like electrodes and means in one of said two last named circuits for shifting the phase of the in-phase wave energy impressed by said local oscillator on said like electrodes relative to the mean phase of the phase modulated wave energy.

14. In a receiving system, a signal carrying wave responsive device, a demodulator coupled thereto and excited by signal carrying wave energy therein, a local oscillator, tuning means connected with said local oscillator, a circuit coupling said local oscillator to said demodulator to impress oscillations thereon, a circuit coupling said local oscillator to said responsive device to supply energy to said oscillator to entrain the same to oscillate at the frequency of the wave, means in one of said two circuits for displacing the phase of the oscillations impressed on said demodulator relative to the mean phase of the signal carrying wave energy impressed on said demodulator and a frequency control circuit coupling said demodulator to said tuning means connected with said local oscillator.

15. In a system for demodulating wave energy modulated in accordance with signals, a pair of demodulator tubes having like input and like output electrodes, means for impressing wave energy to be modulated in phase opposition on like input electrodes of said demodulator tubes, a local oscillator, a circuit coupling said local oscillator to like electrodes in said demodulators for impressing oscillations in phase on said like electrodes, a circuit for impressing modulated wave energy on said local oscillator for entraining the same to produce oscillations in synchronism with said wave energy and phase shifting means in one of said circuits for producing a phase displacement between the energy impressed from said local oscillator on said like electrodes of said demodulators and the signal carrying wave energy impressed in phase opposition on like input electrodes of said demodulators.

16. In a receiving system, a signal carrying wave energy responsive device, a demodulator coupled thereto and excited by signal carrying wave energy in said responsive device, an oscillator including an oscillatory circuit in which oscillations are produced, a circuit coupling said oscillatory circuit to said demodulator to impress produced oscillations on said demodulator, a circuit coupling said oscillatory circuit to said Wave energy responsive device to supply energy to said oscillatory circuit to entrain the same to produce oscillations of the mean frequency of the signal carrying wave energy, and means in one of said circuits for displacing the phase of the oscillations impressed on said demodulator relative to the phase of the signal carrying wave energy impressed on said demodulator.

17. The method of demodulating a wave modulated in phase by means of a pair of detector tubes having like electrodes and a receiving means including a tunable circuit which includes the steps of, applying phase modulated wave energy 4 to be demodulated to like electrodes in said detector tubes, producing oscillatory energy, entraining the produced oscillatory energy by said phase modulated wave energy in phase displaced relation, applying said produced phase displaced oscillatory energy to like electrodes in said detector tubes, one of said applied energies being applied in phase to the like electrodes, the other of said applied energies being applied in phase displaced relation to said like electrodes, and controlling the tuning of said tunable circuit by energy produced in the outputs of said detectors. 18. The method of demodulating wave energy modulated in phase in accordance with signals by means of a demodulator having input and output electrodes which includes the steps of, applying the said phase modulated wave energy to the input electrodes in said demodulator, producing oscillatory energy, entraining the said produced oscillatory energy by said phase modulated energy in phase displaced relation, applying said produced phase displaced oscillatory energy to electrodes in said demodulator, and deriving energy resulting from said demodulation process from the output electrodes of said demodulator.

19. The method of demodulating wave energy modulated in phase in accordance with signals by means of a demodulator having input and output electrodes which includes the steps of, applying said phase modulated wave energy to the input electrodes of said demodulator, producing oscillatory energy, entraining the produced oscillatory energy by said phase modulated wave energy in phase displaced relation, applying said produced phase displaced oscillatory energy to electrodes in said demodulator, maintaining the frequency of said phase modulated wave energy substantially constant during said demodulation process and deriving energy resulting from said demodulation process from the output electrodes of said demodulator.

20. In combination, a source of phase modulated waves, a detector, a circuit feeding waves from said source to said detector, an oscillation generator adjusted to produce waves of mean frequency relative to the frequency of the waves present in said source, a circuit connected to said source for isolating waves of mean frequency, said last mentioned circuit being coupled to said oscillation generator to entrain the oscillations produced thereby in fixed phase relationship with respect to waves of mean frequency of said source, a circuit for feeding waves from said oscillation generator to said detector, and another circuit connected to said detector for utilizing the output of said detector derived from the waves fed thereto.

21. Apparatus as claimed in claim 20, characterized by the provision of an additional circuit for maintaining the frequency of said oscillation generator at a frequency corresponding to the mean frequency of waves in said source of phase modulated waves.

22. In combination, a source of modulated Waves, a first oscillation generator, a circuit controlling the frequency of operation of said generator, means for beating waves from said generator and waves from said source to suitable beat frequency Waves, a second oscillation generator operating at the mean frequency of the frequency of the beat frequency waves produced, a circuit for isolating waves of mean beat frequency from said beat frequency waves, said isolating circuit being coupled to said beat frequency producing means, means utilizing said isolated waves to entrain said second oscillation generator in phase synchronism therewith, means combining said phase synchronized oscillations with said beat frequency oscillations, means for utilizing energy of the combined Waves, and means connected with said beating means and said circuit for controlling the frequency of operation of said generator to automatically frequency control said first oscillation generator.

MURRAY G. CROSBY. 

